1. Field of the Invention
This invention relates to a process of providing an elongate underground cavity having a large volume, particularly in the construction of underground railroad stations having at least two stories, or to provide cavities for superposed or intersecting underground traffic routes.
2. Description of the Prior Art
In the prior art such large-volume cavities have been provided as far as possible by cut-and-cover construction work. For that purpose it is necessary to excavate a pit having virtually the same area as the entire bottom surface of the cavity and then to install the internal fixtures and the means for supporting the walls and the top of the cavity. Thereafter the pit is filled up to the original surface level. In a modification, known as cover-shielded construction work, an excavation is initially made only to the level of the ceiling of the desired cavity and a structural cover of concrete is installed there, whereafter the pit is optionally refilled and the region under the cover is excavated and removed by a mining technique under the cover. In that construction method the pit is open only for a shorter time but the same basic disadvantages will arise as in the first-mentioned known method of construction because an open pit is required, which is susceptible to influences of the weather and particularly in urban regions will interfere with the traffic and will result in a destruction of the environment and/or in damage to roads and buildings.